1. Field of the Invention
The invention relates to a sub-frame for a motor vehicle and, more particularly, to a modular sub-frame for a heavy-duty axle mounting wherein a bottom center casting may be changed to adapt the sub-frame to various steering systems.
2. Description of Related Art
When installing an independent front suspension axle into a heavy duty vehicle with a xe2x80x9cCxe2x80x9d channel or space frame type chassis, a sub-frame is usually required to adapt the independent front suspension axle to the chassis. The sub-frame has the advantage that it forms a complete axle module framework, but it must be revised to fit each chassis configuration.
Conventional sub-frame assemblies are designed to adapt independent front suspensions to a specific chassis design using welded steel plates and tubes. This conventional design tends to be unduly heavy and problems are encountered due to welding distortions. Moreover, there is limited flexibility to adapt these conventional sub-frame designs to various steering systems and chassis configurations.
Moreover, even though the independent front suspension axle can incorporate rubber control arm pivot points and can use an air bag type spring, road noise and vibration are transmitted from the independent front suspension to the chassis.
The need exists for a versatile sub-frame design that can be readily adapted to different chassis configurations and that reduces the amount of noise and vibration transmitted to the chassis.
The present invention is a modular sub-frame design formed as an upper portion for mounting to the chassis and a lower portion using light-weight metal, e.g., aluminum, casting or castings for mounting to the steering components, whereby these two portions are separated by a vibration-dampening bushing. The lower portion supports the steering system and is adaptable to standard automotive bell crank/idler linkages, integral steering gear/idler linkages, and rack-and-pinion steering systems.
In a first preferred design, the lower portion of the modular sub-frame is a one-piece cast member isolated from the upper portion and the chassis by a rubber mounting bushing.
In a second preferred design, the lower portion is a multi-piece casting design where the casting members are jointed by bolts or other fastening means. In the multi-piece casting design, the front and rear bulkhead castings are the same identical part as are the top longitudinal members to provide interchangeability among the various components.
With this design, the lower half of the sub-frame can be highly tooled for low cost and improved dimensional reliability. The upper half of the sub-frame can be tooled with a lower volume manufacturing process to save on capital investment.
The design of this invention adds flexibility for various chassis configurations while maintaining a constant suspension mounting framework.
The invention also provides for a lower bolted plate that can be removed for engine service. A separate bracket can be used to mount the upper control arm to the lower sub-frame so that caster angle and percent anti-dive can be changed to suit specific chassis requirements.
By splitting the sub-frame into two parts, the top part can be isolated from the bottom part to reduce noise transmission from the sub-frame to the chassis, while maintaining the necessary rigid positioning of the suspension control arms and steering system. Also, the top part of the sub-frame can be readily revised to adapt to various chassis configurations without having to revise the bottom part of the sub-frame.
These and other benefits provide by the instant invention will be apparent from the following description and associated drawings.